Neurogenesis is an essential developmental process in which neural progenitors generate neurons. In the developing cerebral cortex, radial glia cells divide symmetrically to self-renew and asymmetrically to generate neurons and other progenitors. We lack a fundamental understanding of the cell biological mechanisms regulating radial glia divisions. In addition, we have a limited understanding of how radial glia divisions ar defined at the molecular level, including the role of post-transcriptional regulation. The overall objective of this proposal is to elucidate the contribution of these essential levels of regulation for neurogenesis, by exploiting a novel mouse neurogenesis mutant. This mutant is haploin-sufficient for Magoh, which is a component of the exon junction RNA binding complex (EJC). Our previous NIH-funded studies demonstrated that Magoh mutants exhibit microcephaly, with brains 30% smaller than normal, largely due to reduced neural progenitors. We found that Magoh is essential for proper mitosis of neural progenitors and discovered that Magoh regulates Lis1, a microtubule-associated protein essential for neurogenesis. Moreover we have found that Magoh controls expression of key neural progenitor determinants. Together, our discoveries point to Magoh as a novel central regulator of neurogenesis, yet we lack a fundamental understanding of how Magoh functions in the brain. We propose Magoh has two critical functions in neural progenitors: to regulate proper mitosis and to act in a post-transcriptional regulatory module controlling expression of key neurogenesis genes. Our central hypothesis is that Magoh regulates asymmetric division of radial glia by influencing the mitotic spindle and mRNA metabolism. To address this hypothesis we will pursue the following aims: First we will determine the cellular mechanism by which Magoh regulates neuron and INP production. We will use conditional genetic analysis along with live imaging of radial glia divisions in live brai slices. Second we will define how Magoh regulates mitosis by elucidating its regulation of microtubules and Lis1. We will determine how Magoh regulates Lis1 levels and if Lis1 functions downstream of Magoh in mitosis. Third, we will define the key mRNA targets of Magoh in neurogenesis and determine the role of the EJC in their regulation. Upon successful completion of these aims, we will have significantly advanced our understanding of how Magoh influences neurogenesis, by regulating both mitosis and mRNAs. Together, our proposed studies will broaden our fundamental understanding of the regulation of asymmetric division and the etiology of neurodevelopmental disorders.